Stabilization of rubbery compositions



Patented July l0,

STABILIZATION OF BUBBERY COMPOSITIONS Leland J. Kitchen, Akron, Ohio, assignor to The Firestone Tire & Rubber Company,

Akron,

Ohio, a corporation of Ohio No Drawing. Application July 25',- 1947, Serial No. 763,758

This invention relates to' the stabilization of rubbery organic compositions, and more particularly to the stabilization without substantial discoloration of rubber-like butadiene polymerizates, and more particularly copolymers of acrylonitrile with butadiene-l,3. The invention includes the process of stabilization and stabilized products, both cured and uncured;

The stabilizers of this invention/include the class of 2,6-di(alpha, alpha, gamma, gamma;- tetramethylbutyl)-4 -alkylphenols in which the alkyl group is preferably methyl but may contain one to about five carbon atoms, such as ethyl, either propyl, any amyl, and may be a mixture such as the product resulting from a process in which alkylation is eif'ecte'd with an alkylating agent in which different butyl or different amyl, etc. groups are present.

The invention includes the stabilization of rubbery copolymers derived from other conjugated dienes than butadiene--1-,3 such as for ex ample copolyniers derived from. is'oprene; 2

cyanobutadiene, cyclopentadiene, piperylene, di

methylbutadiene, Z-methyl-Llbpentadiene; etc. The invention includes also the stabilization of rubbery copolymers of a conjugated diene and compounds having the formula CH2=C(R)--CX when R is H, CH3, CzHs, Cal-1'1 or Cl and-X is -CN, CONH2, -COOR, or -COR when R is an alkyl group which contains one to five carbon atoms. Reference is made to a copending application made jointly by me and George E. P. Smith, Jr Serial No. 653,425, filed March 9, 1946, containing related subject matter.

The stabilizer may be used in amounts of. 0.1

to about percent. Ordinarily in the neighbor hood of 2 to 4 percent will be employed. In the. stabilization of synthetics the stabilizer may advantageously be added to the latex so as to be effective during drying of the latex as well as thereafter. If preferred it may be compounded with thedried rubber on the mill.

The following example illustrates one method of preparing the'preferred stabilizer.

EXAMPLE 1 3- Claims. (-Cl. 260-4535) agitation with 30' percent NaOH solution. The oily layer was analyzed fractionation through a column packed with Raschig rings, having an efliciency of about five theoretical plates. Eightyone grams of the 2,6-di (alpha,- alph'a, gamma, gamma-tetramethylbutyl)-4 methylphenol were recovered as a light yellow, highly viscous liquid boiling at' 168-195 C. at 5 millimeters. After two recrystallizations from methanol the product has a melting point of 5'1.6=52.2 C. The compound is sometimes referred to herein as 2,6-d-i-tertiaryoctyl-4-methylphenol.

The other stabilizers of this invention may be similarly prepared using the appropriate starting phenol.

Various test data on the stabilization of various rubbery compositions, cured and uncured, follow. The control stabilizers used" in the tests recorded are phenyl-beta-naphthylamine (designated PBN in the following tables) and a heptylated diphenylamine. These are two of the most widely used' stabilizers for butadiene polymerizates, but are objectionable because they discolor; The stabilizers of this invention are' shown by the reported experiments to be superior to these commercial stabilizers because they discolor less, and may be classed as non-discoloringstabilizers.

In what'r'ollows; the preferredistabilizer of this invention, 2, 6-di-tertiary octyl-4-metliylphenol, was employed and is referred to in the tables as 2, 6-4.

EXAMPLE 2- Two percent of the preferred stabilizer was added to a latex ofthe rubbery copolymer of butadiene' and styrene commercially known as- GR-S; 0n drying atany elevated temperature which would be usedcormnerciall'y the stabl lizer prevents or inhibitsdiscoloration; The'd'ried' products'wereaged'two days'at C. with the" following results:

Table 11-OopoliJmer aging Stabilizer Properties of Aged Oopolymers Quality Color Very poor Medium brown. Good. Do. Very gcod Dark brown.

The stabilizer of this invention is thus shown to impart age resistance without the discolori'n'g' tendency of phenyl-beta-naphthylamine.

EXAMPLE 3 Two percent of the preferred stablizer of this invention and phenyl-beta-naphthylamine were added respectively to two different portions of a latex of rubbery copolymer from butadiene and acrylonitrile, with thirty percent acrylonitrile content. On drying the latter turned brown while there was no substantial discoloration of the former. The stabilizer is efiective during drying at any elevated temperature without substantial discoloration. The dried products were aged ten days at 95 C. The properties of the two products are reported in the following table. The break-down time is a measure of the amount of set-up which has occurred as determined by the time required to break the material down on a will.

Table 2.--Coplymer aging A similar test was conducted on rubbery copolymer obtained from butadiene and acrylonitrile, but containing 36% acrylonitrile. The test also included a blank. The following table shows the results of aging the dried latices 4 days at 90 C.

' Table 3.-C0polymer aging Aged Prod- Color before Properties of Stabilizer aging Color llfllitgoonlldl None Light tan. Dirty brown Very poor. 2, do Light brown. Very good. PBN I. Brown Dark brown... Do.

Thus, the stabilizers of this invention are effective and relatively non-discoloring stabilizers for the latex coagulum.

EILAMIPIE 5 Dried, stabilized latices prepared as in Example 3 were compounded according to the followin formula:

Copolymer plus stabilizer 100.0 Stearic acid 3.5 Zinc oxide 5.0 Carbon black (E. P. C.) 40.0 Sulfur 2.0 Accelerator -1 1.3

The stocks were cured for eighty minutes at 274 E. On testing they were found to have the properties recorded in Table 4. (In Tables 4-7, the figures for tensile and modulus refer to pounds per square inch, and those for elongation refer to per cent elongation).

Table 4.Vulcanizate Stabilizer Present 2, 6-4 PBN Modulus at 300% Elongation 750 625 Tensile at Break. 2, 825 2, 975 Elongation at Break 620 650 4 These stocks were air bomb aged (60 pounds of air per square inch) for 10 hours at 260 F. The aged properties are recorded in the following table.

Table 5.Aged vulcanizate Stabilizer Present 2, 6-4 PBN Modulus at 300% Elongation 2,076 2, 275 Tensile at Break 2, 625 3, 175 Elongation at Break 350 380 Identical stocks were aged 4 days at 212 F. The aged properties are recorded below.

Table 6.Aged vulcanizate ing to the formula given in Example 5. The properties of the aged stocks after curing are given below:

Table 7.Aged vulcanizate Stabilizer Present 2, 6-4 PBN Modulus at 300% Elongation 900 975 Tensile at Break 3, 462 3, 425 Elongation at Break 650 630 The results of Examples 3-6 show that 2,6-ditertiary-octyl-4=-methylphenol affords excellent protection to rubbery butadiene-acrylonitrile copolymers, and that protection is afforded both the uncured copolymer' and its vulcanizate.

EXAMPLE '7 Rubbery butadieneacrylonitrile copolymer containing about thirty percent acrylonitrile was used in the next test. Two percent of phenylbeta-naphthylamine, heptylated diphenylamine (designated as H. D. in Table 8), and the preferred stabilizer of this invention were added to three different portions of a latex of the copolymer. These latices and another portion which contained no stabilizer were dried and then compounded according to the following formula:

Copolymer (with or without stabilizer) 100.0 Coumarone resin 7.5 Sulfur 1.0 Magnesium oxide 5.0 Zinc oxide 85.0 Neutral clay 20.0 Titanium dioxide 20.0 Accelerator 1.3

The stocks were cured 40 minutes at 280 F. and then subjected to exposure tests. In one test samples were exposed in a fadeometer for ten hours at F. In the other test difierent samples were exposed to a sun lamp for sixteen hours at a distance of seven inches. The following table records the color of the several samples after such exposures.

Table 8.E:cpo-sure tests on copolymer vulcanizate Stabilizer Fadeometcr Test Sun-Lamp Test None Light cream Very ht cream. 2, 64 Very light cream Off white. PBN. Brown Gray brown. H. D Light tan tinge... Light tan.

The stock stabilized with the stabilizer of this invention discolored less than similar stock con-' taining no antioxidant, and became discolored much less than the stocks stabilized with the commercial stabilizers.

Thus the stabilizers of this invention are effective with rubbery compositions, before and after curing. They stabilize the synthetic latices during drying. The invention is defined in the appended claims.

' What I claim is:

1. A rubbery copolymer of butadiene and acrylonitrile stabilized with a relatively small amount of 2,6-di-tertiary-octyl-4-alkylphenol in which the alkyl group contains one to about five carbon atoms.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,260,683 Robbins et a1. Oct. 28, 1941 2,298,660 Stevens et al. Oct. 13, 1942 2,379,482 Frolich July. 3, 1945 2,445,735 Kitchen July 20, 1948 2,470,447 Van Gilder May 17, 1949 2,471,887 Nelson May 31, 1949 

1. A RUBBERY COPOLYMER OF BUTADIENE AND ACRYLONITRILE STABILIZED WITH A RELATIVELY SMALL AMOUNT OF 2,6-DI-TERTIARY-OCTYL-4-ALKYLPHENOL IN WHICH THE ALKYL GROUP CONTAINS ONE TO ABOUT FIVE CARBON ATOMS. 